Implantable living tissue stimulators

Abstract

An implantable living tissue stimulator is described with a current conductive protective shield, to prevent the flow of currents to or from the stimulator circuitry via the electrically conductive body fluid. Also disclosed is an implantable living tissue stimulator of the rechargeable type in which the stimulator circuit components are surrounded by a pickup coil, designed to pick up an external magnetic field for recharging the power source, e.g., battery of the stimulator. One embodiment incorporates one or more ferrite slabs extending through the coil wound about the rest of the stimulator components, in order to increase the coil pick up efficiency and to divert the magnetic field from the stimulator metal components, such as a metal container in which the stimulator circuitry is hermetically sealed and thereby minimize the heating of the components and/or metal container. Also disclosed is a stimulator in which the coil, wound about the stimulator circuit components and the ferrite slabs, is sealed within a ceramic or glass hermetic container which is impervious to body saline fluid or gases.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
       1. In an implantable living tissue stimulator of the type comprising a plurality of stimulator circuit means which form the stimulator circuitry and include at least a power source and pulse generating means powered by said power source to provide pulses adapted to be applied to body tissue to be stimulated, with at least some of the stimulator circuit means being exposable to body saline fluid when said stimulator is implanted in a body, the improvement comprising: current conductive shield means surrounding at least the stimulator circuit means which is exposable to body saline fluid, and connected to a reference potential in said stimulator circuitry for substantially inhibiting the flow of current via body saline fluid to or from said circuit means which are exposable to the body saline fluid, by conducting said current to said reference potential.   
     
     
       2. The improvement as described in claim 1 wherein the stimulator circuit means exposable to said body saline fluid is a coil adapted to have a current induced therein by an alternating magnetic field applied external to the body. 
     
     
       3. The improvement as described in claim 2 wherein said shield means includes at least a first current conductor means surrounding substantially the entire coil exposable to the body saline fluid, with electrically insulating matter between said coil and said first current conductor means, the latter having a first end surrounding a first end of said coil connected to said reference potential and extending to a free floating second end near the second end of said coil. 
     
     
       4. The improvement as described in claim 3 wherein said shield means includes a second current conductor means spaced apart from said first conductor means with electrical insulation matter therebetween, said second conductor means surrounding a portion of said coil from the second end thereof, said second conductor means having a first end which is connected to said reference potential and which surrounds the second end portion of said coil, said second conductor means extending from its first end toward a second free-floating end, with at least a portion of said coil being surrounded by both said first and second conductor means. 
     
     
       5. The improvement as described in claim 1 wherein all of said stimulator circuit means are exposable to body saline fluid, with said current conductive shield means surrounding all of said stimulator circuit means, for substantially inhibiting the flow of currents via the body saline fluid to or from any of the stimulator circuit means. 
     
     
       6. The improvement as described in claim 5 wherein said plurality of stimulator circuit means include at least one coil in which a current is induceable by an alternating magnetic field external to said body. 
     
     
       7. The improvement as described in claim 6 wherein said plurality of stimulator circuit means include recharging means and a pickup coil connected to said recharging means for recharging said power source with the current induced in said pickup coil by the external alternating magnetic field. 
     
     
       8. The improvement as described in claim 7 wherein said power source, said recharging means and said pulse generating means are encapsulated in encapsulating matter which is not impervious to body saline fluid with said pickup coil being wound thereabout, with said shield means surrounding said pickup coil and the encapsulating matter. 
     
     
       9. The improvement as described in claim 8 further including matter means having high magnetic permeability, extending through said pickup coil, for diverting a substantial portion of the magnetic field which passes through said coil from the power source, said recharging means and said pulse generating means which are in said encapsulating matter about which the coil is wound. 
     
     
       10. The improvement as described in claim 1 wherein said plurality of stimulator means include recharging means and a pickup coil in which a current is induced by an external alternating magnetic field for activating said recharging means to recharge said power source, the improvement including a hermetic container for hermetically sealing said recharging means, said power source and said pulse generating means from the body saline fluid, with said pickup coil being external to said hermetic container and connectable therethrough to said recharging means, said pickup coil being surrounded by said shield means. 
     
     
       11. The improvement as described in claim 10 wherein said pickup coil is wound about said hermetic container. 
     
     
       12. The improvement as described in claim 10 wherein said hermetic container is a biocompatible metal, with said pickup coil being wound about it. 
     
     
       13. The improvement as described in claim 12 further including matter means with high magnetic permeability extending through said pickup coil adjacent said hermetic metal container for diverting a substantial portion of the magnetic field which passes through said coil from the hermetic metal container about which the coil is wound. 
     
     
       14. In an implantable living tissue stimulator of the type comprising a plurality of stimulator circuit means which form the stimulator circuitry and include at least a power source, pulse generating means powered by said power source to provide pulses adapted to be applied to tissue to be stimulated, a coil and a circuit connected to said coil and responsive to a current induced in said coil by an alternating magnetic field external to said body, the improvement comprising: said coil being wound about at least some of said stimulator circuit means; and   matter means of high magnetic permeability extending through the coil for at least diverting a substantial portion of the magnetic field which passes through said coil from the stimulator circuit means about which the coil is wound, the dimension of said matter means along the longitudinal axis of said coil, being not less than the extent of the stimulator circuit means about which said coil is wound, along said longitudinal axis.   
     
     
       15. The improvement as described in claim 14 wherein said circuit to which the coil is connected is a circuit for recharging said power source with the current induced in said coil by the external alternating magnetic field. 
     
     
       16. In an implantable living tissue stimulator of the type comprising a plurality of stimulator circuit means which form the stimulator circuitry and include at least a power source, pulse generating means powered by said power source to provide pulses adapted to be applied to tissue to be stimulated, a coil and a circuit connected to said coil and responsive to a current induced in said coil by an alternating magnetic field external to said body, the improvement comprising: said coil being wound about at least some of said stimulator circuit means; and   matter means of high magnetic permeability extending through the coil for at least diverting a substantial portion of the magnetic field which passes through said coil from the stimulator circuit means about which the coil is wound, said high magnetic permeability matter means being exposed on at least two sides of the stimulator circuit means about which the coil is wound.   
     
     
       17. The improvement as described in claim 16 wherein said circuit to which the coil is connected is a circuit for recharging said power source with the current induced in said coil by the external alternating magnetic field. 
     
     
       18. The improvement as described in claim 17 further including a hermetic metal container for hermetically sealing all of said stimulating circuit means except said coil from body saline solution with said coil being wound about said hermetic metal container and said matter of high magnetic permeability which extends along at least two sides of said hermetic metal container. 
     
     
       19. The improvement as described in claim 16 further including a hermetic container for hermetically sealing said stimulator circuitry, said coil and said high magnetic permeability matter, said hermetic container being formed of implantable type ceramic like material which is impervious to body saline fluid and gases. 
     
     
       20. The improvement as described in claim 19 wherein said circuit to which the coil is connected is a circuit for recharging said power source with the current induced in said coil by the external alternating magnetic field. 
     
     
       21. The improvement as described in claim 20 wherein said high magnetic permeability matter means extends through said coil on at least two opposite sides of the stimulator circuit means about which said coil is wound. 
     
     
       22. The improvement as described in claim 16 wherein said high magnetic permeability matter means extends through said coil on at least two opposite sides of the stimulator circuit means about which said coil is wound. 
     
     
       23. The improvement as described in claim 16 wherein all of said stimulator circuit means are surrounded by said high magnetic permeability matter means with said coil being wound about said high magnetic permeability matter means. 
     
     
       24. The improvement as described in claim 23 wherein said circuit to which the coil is connected is a circuit for recharging said power source with the current induced in said coil by the external alternating magnetic field. 
     
     
       25. In a living tissue stimulator of the implantable type including a power source and rechargeable means for recharging said power source by responding to an external magnetic field and pulse generating means powered by said power source to provide pulses adapted to be applied to body tissue to be stimulated, the improvement comprising: current conductive shield means surrounding said stimulator for inhibiting the flow of current from said stimulator or thereto via the body fluid when said stimulator is implanted, said shield means defining a plurality of current conductive members each of which is electrically connected to a reference potential of said power source, said current conductive members being spaced apart from one another whereby any current flowing to or from said stimulator via the body fluid is conducted to said reference potential by at least one of said current conductive members, with any substantially square area on the surface of any of said members being less than the total conductive surface area of said members, by a factor n, where n is not less than 100.